Two Efficient Methods for Replacement of Sulfur by Oxygen in a Thionolactone

Abstract

Selective methods for conversion of thionoesters or thiono-lactones to the corresponding ordinary esters or lactones through replacement of sulfur by oxygen are generally lacking, apart from the long known reaction using aqueous silver nitrate¹ and related processes with lead¹ or mercury² carboxylates. Our recent preparation of bicyclic thionolactone 1 ³ affords a convenient substrate for examination of possible reagents for this transformation. A particularly useful property of 1 is that tetrahedral intermediates 2 and 3, formed on nucleophilic addition of Nu⁻ to 1, have a stereoelectronically favored^3,4 pathway for cleavage of the lactone bridge. Such cleavage in 1 is effectively irreversible, since it will be quickly followed by inversion to the stable diequatorial conformer of cis-3-hydroxycyclohexaneacetic acid (4) or an appropriate derivative, depending on the specific nature of Nu⁻. This feature makes 1 a sensitive test of methods for replacement of sulfur by oxygen without competing rupture of the lactone ring.